Keyboard In The Wilderness schreef:

Ah OK a trick question no less

Turn about is fair play -- (but not too tricky)

On an AM radio -- one hears a station broadcasting on the tuned
frequency -- but also another station is heard that is broadcating on an
entirely different frequency !!!

Ignoring a strong adjacent channel station -- how is this possible ???

It is called mirror frequency interference.

When you receive say 540, your local oscilator produces 540 + 450 = 990
kHz. In the mixer 540 and 990 produces 990-540 = 450 (and 540+990, this
is almost fully rjected)
But suppose there is a strong signal on 1440 that is also coming into
your mixer you will find that this also produces the IF of 450 kHz,
since 1440 - 990 = 450.
So now you will hear the 540 and 1530 station; only good radio's have
proper antenna filters to reject the 1530 signal.


BTW: do US digitally controlled receivers have 87.9 ?
ruud

But

--
Keyboard mired in the political rants here (;-)

"Radioman390" wrote in message
...
Well, it was a trick question, but you got it right.

There was a potential second answer (maybe more) which has to do with the
phrasing I used which said I was one mile from the campus, and could see
the
antenna. Well, maybe the antenna was far away (on a mountain top) and I
was
out-of-range of the signal.

But my thinking in posing the mind-twister was that I didn't know the FCC
had
actually granted three licenses for 87.9 (two translators and KSHR), and
only
noticed while doing a search of the FCC database.

www.fcc.gov/mb
on the left side is a box marked "shortcuts"; scroll down to "FM query",
and
then click on "start shortcut"